dhcpv4: Add OptRootPath (#163)

* dhcpv4: Add OptRootPath

Adds a root path option that supports DHCPv4 option 17

* Add root path parsing to giant option parsing switch

4 files changed, 107 insertions, 0 deletions

diff --git a/dhcpv4/option_root_path.go b/dhcpv4/option_root_path.go
new file mode 100644
index 0000000..504ed17
--- /dev/null
+++ b/dhcpv4/option_root_path.go
@@ -0,0 +1,52 @@
+package dhcpv4
+
+import (
+	"fmt"
+)
+
+// This option implements the root path option
+// https://tools.ietf.org/html/rfc2132
+
+// OptRootPath represents the path to the client's root disk.
+type OptRootPath struct {
+	Path string
+}
+
+// ParseOptRootPath constructs an OptRootPath struct from a sequence of  bytes
+// and returns it, or an error.
+func ParseOptRootPath(data []byte) (*OptRootPath, error) {
+	// Should at least have code and length
+	if len(data) < 2 {
+		return nil, ErrShortByteStream
+	}
+	code := OptionCode(data[0])
+	if code != OptionRootPath {
+		return nil, fmt.Errorf("expected option %v, got %v instead", OptionRootPath, code)
+	}
+	length := int(data[1])
+	if len(data) < 2+length {
+		return nil, ErrShortByteStream
+	}
+	return &OptRootPath{Path: string(data[2 : 2+length])}, nil
+}
+
+// Code returns the option code.
+func (o *OptRootPath) Code() OptionCode {
+	return OptionRootPath
+}
+
+// ToBytes returns a serialized stream of bytes for this option.
+func (o *OptRootPath) ToBytes() []byte {
+	return append([]byte{byte(o.Code()), byte(o.Length())}, []byte(o.Path)...)
+}
+
+// String returns a human-readable string for this option.
+func (o *OptRootPath) String() string {
+	return fmt.Sprintf("Root Path -> %v", o.Path)
+}
+
+// Length returns the length of the data portion (excluding option code and byte
+// for length, if any).
+func (o *OptRootPath) Length() int {
+	return len(o.Path)
+}
diff --git a/dhcpv4/option_root_path_test.go b/dhcpv4/option_root_path_test.go
new file mode 100644
index 0000000..53de45b
--- /dev/null
+++ b/dhcpv4/option_root_path_test.go
@@ -0,0 +1,46 @@
+package dhcpv4
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestOptRootPathInterfaceMethods(t *testing.T) {
+	o := OptRootPath{Path: "/foo/bar/baz"}
+	require.Equal(t, OptionRootPath, o.Code(), "Code")
+	require.Equal(t, 12, o.Length(), "Length")
+	wantBytes := []byte{
+		byte(OptionRootPath),
+		12,
+		'/', 'f', 'o', 'o', '/', 'b', 'a', 'r', '/', 'b', 'a', 'z',
+	}
+	require.Equal(t, wantBytes, o.ToBytes(), "ToBytes")
+}
+
+func TestParseOptRootPath(t *testing.T) {
+	data := []byte{byte(OptionRootPath), 4, '/', 'f', 'o', 'o'}
+	o, err := ParseOptRootPath(data)
+	require.NoError(t, err)
+	require.Equal(t, &OptRootPath{Path: "/foo"}, o)
+
+	// Short byte stream
+	data = []byte{byte(OptionRootPath)}
+	_, err = ParseOptRootPath(data)
+	require.Error(t, err, "should get error from short byte stream")
+
+	// Wrong code
+	data = []byte{43, 2, 1, 1}
+	_, err = ParseOptRootPath(data)
+	require.Error(t, err, "should get error from wrong code")
+
+	// Bad length
+	data = []byte{byte(OptionRootPath), 6, 1, 1, 1}
+	_, err = ParseOptRootPath(data)
+	require.Error(t, err, "should get error from bad length")
+}
+
+func TestOptRootPathString(t *testing.T) {
+	o := OptRootPath{Path: "/foo/bar/baz"}
+	require.Equal(t, "Root Path -> /foo/bar/baz", o.String())
+}
diff --git a/dhcpv4/options.go b/dhcpv4/options.go
index 02fa6e4..6256ef7 100644
--- a/dhcpv4/options.go
+++ b/dhcpv4/options.go
@@ -80,6 +80,8 @@ func ParseOption(data []byte) (Option, error) {
 		opt, err = ParseOptVIVC(data)
 	case OptionDNSDomainSearchList:
 		opt, err = ParseOptDomainSearch(data)
+	case OptionRootPath:
+		opt, err = ParseOptRootPath(data)
 	default:
 		opt, err = ParseOptionGeneric(data)
 	}
diff --git a/dhcpv4/options_test.go b/dhcpv4/options_test.go
index 899fb2c..c06f6f5 100644
--- a/dhcpv4/options_test.go
+++ b/dhcpv4/options_test.go
@@ -144,6 +144,13 @@ func TestParseOption(t *testing.T) {
 	require.Equal(t, OptionClientSystemArchitectureType, opt.Code(), "Code")
 	require.Equal(t, 4, opt.Length(), "Length")
 	require.Equal(t, option, opt.ToBytes(), "ToBytes")
+
+	option = []byte{17, 4, '/', 'f', 'o', 'o'}
+	opt, err = ParseOption(option)
+	require.NoError(t, err)
+	require.Equal(t, OptionRootPath, opt.Code(), "Code")
+	require.Equal(t, 4, opt.Length(), "Length")
+	require.Equal(t, option, opt.ToBytes(), "ToBytes")
 }
 
 func TestParseOptionZeroLength(t *testing.T) {